Function coeffX

src/compute-engine/rubi/rubi-utils.ts:3210–3213

Coefficient of xᵏ in a constant/linear expr (0 when absent).

(u: Expression, x: string, k: number)

 * else null. */
function classifyFactor(
  ce: ComputeEngine,
  f: Expression,
  x: string
): Factor | null {
  let exp: Expression = ce.One;
  let base = f;
  if (f.operator === 'Power' && f.ops) {